A number of prior patents have addressed the problem of minimizing arcing or sparking. An early use for such circuits was in connection with attempting to limit the arcing at contacts of a switch as the switch was opened or closed, for example, in U.S. Pat. No. 3,075,124, which utilizes a transistor in series with the switch. U.S. Pat. No. 3,614,464 is also concerned with suppressing arcs at contacts and utilizes a semiconductor switch in series with one set of contacts and in parallel with another set of contacts.
More recently, circuits to protect a switching transistor which is attempting to turn off an inductive load have been devised, for example, as shown in U.S. Pat. No. 3,729,655. U.S. Pat. No. 3,912,941 also utilizes a transistor to minimize arcing across contacts, in this case, of a relay. U.S. Pat. No. 4,025,820 is directed to a circuit attempting to minimize arcing at contacts as the contacts are opened.
U.S. Pat. No. 4,062,051 utilizes a thyristor in series with a battery-energized load which is stated to prevent significant arcing across partially open contacts.
U.S. Pat. No. 4,241,369 utilizes a thyristor in a circuit for charging a capacitor in an electronic flash unit and detects the presence of an arc across the mechanical switch contacts to turn off the thyristor.
U.S. Pat. No. 4,251,845 utilizes a triac and thyristors to suppress the arc across load carrying contacts of a relay.